The present invention relates to self-powered radiation detectors such as are used for nuclear reactor incore radiation monitoring. The term self-powered detector indicates that no external drive potential is required for operation of the detector, as is the case for ion-chamber or other such more conventional radiation detector. Self-powered detectors typically have a compact rugged, small diameter, tubular structure which is easily incorporated in the reactor core.
The prior art self-powered detector designs are basically a coaxial design with a center conductor termed the emitter electrode insulated from a tubular outer conductor termed the collector electrode. The emitter and collector electrodes are formed of different materials which have significantly different responses or interactions with radiation flux, which in a reactor can be neutron flux or gamma flux. The emitter and collector electrode materials are selected for their relative neutron or gamma flux interaction capabilities. A neutron responsive self-powered detector is described in U.S. Pat. No. 3,940,627, with a metal layer about a cylindrical emitter electrode. The metal layer is relatively neutron insensitive and the metal layer and the emitter are electrically common, and this structure reduces the effect of interfering signals which are not neutron flux related. In U.S. Pat. No. 4,008,399 a radiation detector is described with two concentric, tubular collector electrode portions which serve to provide a gamma compensated device.
The significant advantage of a self-powered detector is its long life reliability capability over prior art radiation detectors, but self-powered detectors have a generally lower sensitivity, which has limited their usage. It is generally desired to increase the sensitivity of self-powered detectors.